Track-type machines such as tractors, track-type loaders, and excavators, may include an undercarriage having a roller frame and a sprocket, as well as a track chain encircled about the sprocket and the roller frame. A power source, such as an engine or a motor, may actuate the rotation of the sprocket which, in turn, may pull the track chain and cause the machine to move. The track chain may include two chain portions on opposing sides of the track chain, and each of the chain portions may consist of a plurality of track links. The chain portions may be interconnected by a plurality of joints linking the track links of the two chain portions. In addition to connecting the two chain portions, the joints may also allow the track chain to bend as it is driven over the components of the undercarriage.
The joints of a track chain may generally include a bushing press fit through the track links on opposing sides of the track chain, as well as a pin inserted through a bore defined by an inner diameter of the bushing. As the track chain moves, the bushing and the pin may rotate with respect to one another. However, wear or galling of the bushing and the pin may be caused by a number of factors such as heavy loads that cause the bushing and the pin to be pressed together. In addition, press fitting of the track links over the bushing may cause deformation of the bushing leading to “pinch points” where the bushing presses or digs into the pin. With extended use and/or use under heavy loads, high internal pressures, oil leakage, and even premature failure of the track chain may eventually result.
One approach to reduce galling effects at the bushing and the pin of track chain joints has been to introduce a larger radius rounded region into the inner diameter region of the bushing that contacts the pin (see U.S. Pat. No. 8,613,486). In particular, the rounded region of the bushing provides a smoother contact surface between the bushing and the pin, thereby reducing galling effects. Another approach involves installing a rounded insert between the bushing and the pin (see U.S. Pat. No. 6,846,051). While effective, it may be expensive and difficult to machine curvilinear or rounded profiles into the inner diameter of the bushing due to limited access to the inner diameter of the bushing. Thus, the manufacture of track chain bushings with such curvilinear inner diameter profiles may require precise control and hard-turning of the bushing inner diameter.
Clearly, there is a need for more cost-effective and efficient approaches for reducing galling of undercarriage track chain bushings and pins.